The present invention concerns a positioning device for after-treatment tools for the after-treatment of parisons produced in an injection molding mold and a system having such a positioning device.
Injection molding is one of the most important processes for the production of moldings or mold parts. In that case the molding material is heated, plasticised and urged under high pressure into a suitable mold tool. The molding material hardens in the mold tool and is then removed from the opened tool.
Commercially available PET bottles are generally produced by stretch blow molding of a hollow body preform or hollow body parison. In that case the hollow body parison is produced in a first step by means of injection molding. The stretch blow molding operation which follows the injection molding procedure can be effected either directly after production of the hollow body parison or at a later time.
The manufacture of the corresponding injection molding molds requires a high level of expenditure as the injection molding mold on the one hand must be designed for very high pressures while on the other hand it must also have suitably heated and/or cooled passages.
Usually an injection molding tool for the production of PET parisons comprises a multiplicity of, for example 96, cavities, into which suitably designed tool cores are introduced. When the tool is closed, that is to say when the core is fitted into the corresponding cavity, a space, referred as the molding space, is formed between the core on the one hand and the cavity on the other hand. The plasticised plastic material, for example PET, is then injected into that space under high pressure. As soon as the PET parison has sufficiently cooled down the mold can be opened and the parison removed.
To reduce the cycle times, that is to say the time from one injection molding operation to the next, it is already usual for the preform to be removed from the mold at a very early moment in time at which the preform is already solid at its outside surfaces, but the internal region thereof, referred to as the core region, is still fluid. In that state the parison is generally transferred into what is referred to as a receiving plate comprising a group of receiving cavities. Thus for example in the case of what are referred to as vertical tools, that is to say those injection molding tools which open by a vertical movement of the one tool portion relative to the other, it is usual for the tool mold to be already opened after for example 10 seconds, for a receiving plate with suitable receiving cavities to be moved into the mold, for the individual preforms to be allowed to drop into the receiving cavities under the effect of the force of gravity, for the receiving plate with the preforms to be moved out of the tool, for the mold to be closed again and for the next injection molding operation to begin. During the next injection molding operation the previous preforms remain in the receiving cavity which is usually cooled.
Embodiments are also known in which the individual preforms are removed from the mold by means of a gripper unit and transferred into the receiving plate arranged outside the tool mold.
As the parison must remain in the receiving cavity of the state of the art for a comparatively long time for cooling purposes so that generally the next parison can already be removed from the injection molding tool before the parison has cooled in the receiving cavity to such an extent that it can be removed without the risk of damage, it is already usual to use receiving plates having a plurality of groups of receiving cavities, wherein each group has as many receiving cavities as the injection molding tool produces parisons in each injection cycle. The individual receiving cavity groups are then fitted with parisons in succession so that the individual parison can remain in the receiving cavity for longer than an injection molding cycle.
Such receiving plates however are correspondingly large and can only be controlled with very great complication and effort.
To further reduce the cycle time, considerable endeavors have been undertaken in recent years to already remove the preform from the injection molding mold at a very early time. As the preform is still relatively soft at such an early time higher demands are made on the after-treatment. Thus it has occasionally already been proposed that the parison held in the receiving cavity is to be additionally cooled or aftertreated with an after-treatment pin which is introduced into the parison. In the known devices with an after-treatment pin however that is only briefly moved into the parison.
WO 03/097326 already discloses a device for the after-treatment of parisons produced in an injection molding mold. That machine has a tool block with two different groups of tool cores. In addition, there are four receiving plates which are arranged on a cube, as well as two pin plates. After the parisons have been produced in the injection molding machine the machine is opened and the tool block rotated in such a way that the other group of tool cores can cooperate with the tool cavities. The parisons produced by means of injection molding are now on the free tool cores. From there they are now transferred into a receiving plate having suitable receiving cavities. The receiving cube with the individual receiving plates is then turned through 90° and a pin plate is briefly introduced into the parisons. Thereafter the pin plate is removed again and the receiving cube is turned through a further 90° and another pin plate is again introduced into the parisons.
The provision of a plurality of after-treatment tools comprising receiving cavities and/or receiving fingers however means that generally a complicated and expensive robot unit is necessary for positioning the individual after-treatment tools.